1. Field of the Invention
The invention relates to a brake mechanism comprising a rotatable annular element mounted on a non-rotatable hub along facing surfaces shaped to increase friction when the annular element is pressed toward a support surface, thereby imparting steady and controllable braking force. The invention is particularly applicable to slowing small moving platforms such as roller skates, skate boards, scooters and similar vehicles which can be tilted to apply the brake to a bearing surface. The brake mechanism also can be arranged on a vertically movable mount for applying the brake, making it applicable to heavier vehicles such as service carts or even large vehicles such as trucks. In addition to providing dynamic braking, the invention is advantageous for rendering supporting platforms immovable when loaded, and movable when unloaded, due to the difference in frictional engagement of the annular element and the hub caused by the change in loading weight.
2. Prior Art
Various forms of wheeled devices that permit a person to traverse a ground surface are known. One class of such devices includes roller skates, skateboards, scooters and similar small vehicles, which have a relatively small platform supported by wheels. The platform can be manipulated by the user in operating the device. Braking stops are often included in vehicles of this type, typically comprising a rubber block or ball that protrudes downwardly at the front or rear of the device at an elevation higher than the lower periphery of the wheels, but which can be pressed against the floor, pavement or other ground surface over which the device moves. Friction between the stop and the ground surface helps to slow the device.
The stop is normally caused to press against the ground surface by tilting the platform around an axis transverse to the direction of motion, until the elevation of the stop is equal to that of the wheels, i.e., bringing the stop into engagement with the ground. By varying the extent of tilting, the user varies the proportion of his or her weight which is borne by the stop, as opposed to being borne by the wheels, and thus varies the frictional force exerted for stopping.
Figure skates (both ice skates and roller skates) generally have a stop at the front or toe end, whereby the user can push off from the toe or fix the toe in position in order to execute a turn or spin. It is also known to place a stop in at the rear, by which the user simply exerts friction in order to slow down or stop. U.S. Pat. No. 2,191,018--Ickenroth, for example, discloses a four wheel roller skate having a soft rubber stop which is pivotally attached to extend rearwardly behind the rear wheel of the skate, at a slightly higher elevation than the wheel. A skater tilts the skate (i.e., raises the toe of the skate higher than the heel) to engage the stop with the skating surface. Braking action is produced by abrasion of the stop on the skating surface. Another example of a rear stop is disclosed in U.S. Pat. No. 2,021,316--Marx, wherein a stop similar to a wheel disposed perpendicular to the direction of movement protrudes to the rear and can be engaged against the ground by tilting the skate. In U.S. Pat. No. 4,181,227--Balstad, a cylindrical toe mounted stop is provided. The stop is fixed against rotation by a through-bolt arranged to enable the position of the stop to be varied as desired.
U.S. Pat. Nos. 5,028,058 and 5,052,701, both to Olson, similarly disclose roller skates having a rear mounted stops. In this case the skates are in-line roller skates having two or more wheels mounted one behind the other, the front and rear wheels being mounted slightly higher than the intermediate wheels so as to define a curve similar to an ice skate blade. The wheels are mounted on a channel-like frame extending along the longitudinal axis of the skate, the wheels being mounted via individual axle pins extending through the channel. In-line skates of this type are popular for outdoor use, typically on concrete or asphalt pavement and the like.
A further possibility is to place a stop at both the front and rear. The front stop permits the user to fix the toe, and the rear stop allows braking while in motion by abrading the rear stop against the skating surface. An example of dual stops is shown in U.S. Pat. No. 4,273,345--Ben-Dor.
Abradable stop devices depend for their stopping ability on the extent of frictional engagement with the skating surface. Of course the skating surface may vary from smooth to irregular and could include any of a multitude of materials having different coefficients of friction. Even on a given stretch of pavement, the user may encounter relatively smoother or rougher sections, affecting the extent to which the abradable stop grabs to the pavement. The skating surface may have a light coating of dirt, gravel or sand which reduces braking action by providing a buffer between the stop and the surface, and provide unpredictable braking results. For very different types of surfaces, e.g., a wood floor vs. an asphalt pavement, the abrading stop will produce quite different braking characteristics.
Abrading stops also have the drawback that as the stop is worn away through abrasion over time, the working surface of the stop becomes higher above the skating surface. The skater will be required to raise the toe of the skate higher in order to engage the stop with the skating surface or to achieve the same force. Therefore, the skater must have the ability to raise the toe of the skate through a range of angles, and cannot become accustomed to a single toe angle for achieving a particular stop engagement. At some point, the stop must be replaced.
U.S. Pat. No. 3,224,785 to Stevenson discloses a form of roller skate supported substantially by a single wheel. A brake arrangement comprises a brake roller mounted on a crank arm and normally disposed above the skating surface and at a space behind the main wheel. When the skate is tilted such that the brake roller engages with the skating surface, the crank arm pivots to move the brake roller into engagement with the main wheel of the skate. Due to contact with the skating surface, both the brake roller and the main wheel seek to rotate in the same direction. However they are forced into contact. Braking action is achieved by either or both of the frictional contact between a surface of the brake roller and a surface of the main wheel, moving in opposite directions, or assuming the brake roller and the main wheel lock, by friction between the brake roller and the skating surface. This skate brake has the drawback that the brake wheel is an abradable element which is subject to wear against both the skating surface and the main wheel. The action also abrades the main wheel. Periodically, the worn elements must be replaced. Further, the braking action is affected by variations in the skating surface as well as by dirt and grit picked up by the brake roller and/or by the main wheel and carried into the nip between them to disrupt smooth application of braking force.
There is a need for a brake mechanism which does not rely either on the bearing surface or on a main bearing wheel of the vehicle, which necessarily picks up dirt from the bearing surface. Such a brake can be protected against dirt and would be unaffected by variable characteristics of the surface. The brake would be particularly useful for applications such as roller skates, skateboards and the like, and also useful for other forms of vehicles. It would be advantageous if such a braking apparatus could be arranged to operate in as convenient a manner as a simple skate brake stop, which is operated by tilting the skate.
The brake according to the invention has friction surfaces which are physically separate from the bearing wheels and the ground engaging portions of the brake. These surfaces thus are protected from dirt and debris. The invention provides a braking roller which does not achieve its primary braking force by abrasion against either the bearing surface or a ground engaging wheel. Instead, the braking roller is designed to engage with the ground surface on an outer surface of the braking wheel, and the frictional contact (i.e., relative motion while in contact) is substantially limited to the engagement between the braking roller and its hub. A particular contour of the friction surface, preferably characterized by opposed conical frustum shapes of the hub and roller, a concave circumferential channel or a convex circumferential shape, allows the user to vary the friction by exerting pressure on the roller in the same manner as with a stop. However, the roller is arranged so as not to slide on the bearing surface and instead to slide substantially exclusively on the hub. Friction is thus provided by the very repeatable interaction of surfaces which are unaffected by dirt or by the character of the surface over which the skate is moving. The friction is thus predictable and constant for a given pressure, with every application of the roller brake.